This invention relates to the selective removal of a metal component from an aqueous stream containing a heat-sensitive component in solution. The invention relates in one aspect to the manufacture of 1,3-propanediol. In one embodiment of this aspect, the invention relates to a cobalt-catalyzed process for preparing 1,3-propanediol in which cobalt is efficiently removed from an intermediate aqueous stream.
1,3-Propanediol is an important industrial chemical which can be prepared in a two-step process in which ethylene oxide is first hydroformylated in organic solution in the presence of a metal catalyst such as a cobalt or rhodium carbonyl, to form 3-hydroxypropanal. The 3-hydroxypropanal intermediate is water extracted under pressure and the cobalt catalyst is recycled to the hydroformylation reaction in the organic phase. The aqueous 3-hydroxypropanal is then hydrogenated to 1,3-propanediol. Ideally, the aqueous 3-hydroxypropanal can be routed directly to the hydrogenation reactor. However, carbon monoxide dissolved in the water is a poison for most heterogeneous hydrogenation catalysts, as is the small amount of metal catalyst which typically leaches into the water phase during extraction of 3-hydroxypropanal. For acceptable product yields, the catalyst must be removed from the aqueous 3-hydroxypropanal solution under conditions which do not degrade the 3-hydroxypropanal.
It is therefore an object of the invention to efficiently remove cobalt and rhodium compounds from an aqueous solution of 3-hydroxypropanal without significant degradation of the 3-hydroxypropanal. In one embodiment, it is a further object of the invention to provide an aqueous 3-hydroxypropanal stream for hydrogenation which is essentially free of carbon monoxide and residual metal compounds.